The present invention relates to the medical diagnostic imaging and surgical arts. It finds particular application in conjunction with image guided surgery (IGS), and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Medical diagnostic imaging is a valuable tool for obtaining accurate visualization of a particular patient""s internal anatomy and/or pathology in a minimally invasive manner. Prior to a medical procedure, three-dimensional (3D) diagnostic image data of the brain, spinal cord, and/or other anatomy of interest is often generated by CT scanners, magnetic resonance imaging (MRI) scanners, gamma cameras, and other medical diagnostic imaging equipment. Typically, these imaging modalities provide structural detail with a resolution of a millimeter or better. Reconstructed images of the patients anatomy are then used by medical personnel to aid in navigating through and/or around various anatomical structures.
Commonly, an IGS system includes a computer, active and/or passive tools carrying infra-red (IR) emitting diodes or reflective spheres, a stereoscopic optical tracking system, and a tool interface device. The IR rays emitted by the active tool (or reflected in the case of a passive tool) are detected by charge-coupled device (CCD) cameras mounted on an optical unit. Using the detected IR rays, the system tracks and/or localizes the position and orientation of the tool in a 3D coordinate space which is registered with that of the 3D image data. In this manner, the position and trajectory of a tool relative to imaged anatomy is determined or visualized and used to aid in the maneuvering of the tool and/or the placement of a tool guide.
Various frameless stereotactic IGS procedures have been developed which take advantage of the 3D image data of the patient. These procedures include guided-needle biopsies, shunt placements, craniotomies for lesion or tumor resection, and the like. Another area of frameless stereotaxy procedure which requires extreme accuracy is spinal surgery, including screw fixation, fracture decompression, and spinal tumor removal.
In spinal screw fixation procedures, for example, surgeons or other medical personnel drill and tap a hole in spinal vertebra into which a screw is to be placed. The surgeon often relies heavily on his own skill in placing and orienting the bit of the surgical drill prior to forming the hole in the vertebra. Success depends largely upon the surgeon""s estimation of anatomical location and orientation in the operative field. Unaided, this approach can lead to less than optimal placement of screws which in turn may injure nerves, blood vessels, or the spinal cord.
Nevertheless, use of a stereotactic IGS procedure presents certain problems and/or complications of its own. For example, one problem is accurately registering anatomy of a subject in real space with its corresponding image in image space. This is especially troublesome in cases where the relative spatial relationships of various anatomical features of interest have shifted or are otherwise changed in comparison to when the image was obtained.
In spinal procedures, for example, it is extremely difficult to ensure that the individual vertebrae of the subject are in the exact same relative position to one another when the procedure is performed as when the image is obtained. This is particularly the case when imaging is done at some time prior to the procedure being performed, and the subject does not remain completely immobilized in the interim. Accordingly, a transform which registers one vertebrae in real space with its corresponding image in image space does not accurately map the other vertebrae to their corresponding images in image space. Likewise, using the same transform to map the position and/or orientation of a surgical tool in the vicinity of different vertebrae, results in less than optimal image space registration of the surgical tool with respect to the nearby anatomy and/or inaccurate visualization of the relative spatial relationship between the surgical tool and the nearby anatomy.
The present invention contemplates a new and improved registration technique which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of mapping a chosen point in real space to its corresponding location in image space is provided. The method includes obtaining a diagnostic medical image of a subject including multiple rigid objects, and individually computing separate transforms which register each of the rigid objects in real space with their corresponding locations in image space. After choosing a target point in real space, the target point is mapped to image space using a designated transform. A number of the rigid objects are selected which are closest to the target point in image space, and an interpolated transform is generated from the separate transforms which correspond to the selected rigid objects. The target point is re-mapped in image space using the interpolated transform, and the interpolated transform is set as the designated transform for subsequent mappings.
In accordance with a more limited aspect of the present invention, the interpolated transform is generated using nearest neighbor interpolation.
In accordance with a more limited aspect of the present invention, the number of rigid objects selected is two.
In accordance with a more limited aspect of the present invention, the number of rigid objects selected is one.
In accordance with a more limited aspect of the present invention, the method is repeated for multiple target points such that each target point is ultimately mapped to image space using its own corresponding interpolated transform.
In accordance with a more limited aspect of the present invention, the target points selected define a surgical tool in real space.
In accordance with a more limited aspect of the present invention, the method further includes rendering an image representation of the surgical tool in image space in accordance with where the target points are mapped to in image space.
In accordance with a more limited aspect of the present invention, when a relative spatial relationship between the multiple rigid objects in real space does not match that of the multiple rigid objects in image space, then the image representation of the surgical tool in image space appears deformed in relation to the surgical tool in real space.
In accordance with a more limited aspect of the present invention, a relative spatial relationship of each target point to its nearest rigid object in image space is substantially identical to that of each target point to its nearest rigid object in real space.
In accordance with another aspect of the present invention, an image guided surgery system is provided. It includes a support on which a subject is positioned in real space, and a human viewable display on which is rendered, in an image space, an image representation of anatomy of the subject. The anatomy includes a plurality of rigid objects. Also included is a surgical tool having points thereon from which radiant energy is directed. A detector unit tracks an orientation and position of the surgical tool in real space via the radiant energy directed therefrom, and a processor maps the orientation and position of the surgical tool from real space into image space using an interpolated transform. The interpolated transform is interpolated from a number of rigid object transforms which each register one of the plurality of rigid objects in real space to its corresponding image in image space.
In accordance with a more limited aspect of the present invention, based on the processor""s mapping, the surgical tool is visualized on the human viewable display along with the image representation of anatomy of the subject.
In accordance with a more limited aspect of the present invention, as visualized on the human viewable display, the surgical tool is deformed to compensate for differences in relative spatial positioning between the rigid objects in real space as compared to image space.
In accordance with a more limited aspect of the present invention, the interpolated transform is interpolated from those rigid object transforms corresponding to a number of the rigid objects closest to where the surgical tool is being mapped to by the processor.
In accordance with a more limited aspect of the present invention, the interpolated transform is interpolated using nearest neighbor interpolation.
In accordance with a more limited aspect of the present invention, the rigid objects are vertebrae.
One advantage of the present invention is accurate mapping of points in real space to image space in the presence of multiple rigid object registration between the two spaces.
Another advantage of the present invention is the preservation of the relative orientations and positions of mapped target points with respect to their nearby anatomy.
Yet another advantage of the present invention is smoothly varying registration for multiple rigid objects.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.